After reading this article you will learn about the definition and characteristics of Electrocardiogram (ECG).
Definition of ECG:
This is the graphic records of the variations in electrical potential caused by electrical activity of the heart muscle and detected at the body surface, as a method for studying the action of the heart muscle.
As the cardiac impulse passes through the heart, electrical currents spread into the tissues surrounding the heart, and a small proportion of these spreads all the way to the surface of the body. If electrodes are placed on the skin on opposite sites of the heart, electrical potentials generated by these currents can be recorded; the recording is known as an electrocardiogram and abbreviated as ECG or EKG.
Characteristics of Normal ECG:
The normal ECG is composed of ‘P’ wave, a ‘QRS’ complex, and a ‘T’ wave. The QRS complex is often three separate waves, the Q wave, the R wave and the S wave.
The P wave is caused by electrical potentials generated as the atria depolarize prior to contraction. The QRS complex is caused by potentials generated when the ventricles depolarize prior to contraction, that is as the depolarization wave spreads through the ventricles.
Therefore, both the P waves and the components of the QRS complex are “depolarization waves.” The T wave is caused by potentials generated as the ventricles recover from the state of depolarization. This wave is known as “repolarization wave.” Thus, the electrocardiogram is composed of both depolarization and repolarization waves.